I find myself wondering to what extent a bullet hitting an apple, or a human skull, is analogous to a scenario in which two objects of similar mass and composition collide. The importance attached to this analogy makes me suspect that there is a greater similarity than I can detect.
Actually, I thought I answered this already,.... but,.... here goes again.
The accurate part of the analogy is the formation of a neat round hole where the impacting planet hits.
The inaccurate part of the analogy is that everything will fly apart.
Apples would fly apart but planets will not.
It's really simple to see this. It's just gravity.
If you put two apples side by side, what happens?
If you put two planets side by side, what happens?
It truly is simple.
Perhaps, stating the obvious (from Newton's formula for gravity) might help;
For a fixed distance of separation, the gravitational force of attraction between two objects, is proportional to the product of their masses.
Make it even simpler. Assume both objects have the same mass.
Then the force, pulling the objects together, is proportional to the mass squared. You get the idea?
